Florida ECS Quick Tips January 2015
Dicot or Monocot? How to Tell the Difference
Flowering plants are divided into two groups - monocots and dicots. Recognizing which of these two
groups a plant belongs to is a great time saver when you are out in the field trying to identify a plant
using a key. The names or these groups are derived from the number of
cotyledons or seed leaves that the embryonic seedling has within its seed. A
monocot, which an abbreviation for monocotyledon, will have only one cotyledon
and a dicot, or dicotyledon, will have two cotyledons. However, this distinction will
not help you when you are trying to determine which group a plant belongs to if it
is no longer a seedling. And, sometimes doesn’t even help if you are looking at a
seedling, because many plants do not bring their cotyledon(s) above the soil
surface when they germinate as the seedling shown to the left did.
Here are some key features to look for to determine whether a plant is a monocot or a dicot.
Leaves of dicots have veins that are branched. Sometimes the veins branch out on either side of the leaf
from a middle vein, in an arrangement resembling a feather (pinnate arrangement) shown in the picture
below left. Other dicots have veins that branch out from a single vein, like
fingers on a hand (palmate arrangement) shown in
the picture to the right. Monocots have veins that
are parallel to one another as shown in the picture
below right. However, this does not mean that all
monocots have narrow grass-like leaves. Arrowhead (left) is a monocot.
Because the leaves have lobes that hang downwards, it almost looks like the
veins branch out in the same manner as described for palmate veins.
However, if you look closely, you can see that all the veins originate at the
base of the leaf and are parallel to each other in each lobe of the leaf.
If your plant is flowering, you can tell if
it is a monocot or dicot by the number
of petals and other flower parts.
Monocots have flower parts in threes
or multiples of threes as shown in the
flowers to the left. Dicots have flower
parts in multiples of fours or fives like
the five-petaled dicot flower pictured
to the right.
Cotyledons
